﻿118 
  DR. 
  A. 
  DTXE0P 
  OB 
  THE 
  JERSEY 
  BRICK-CLAY. 
  

  

  6. 
  On 
  the 
  Jersey 
  Brick-Clay. 
  By 
  Axdrew 
  Destop, 
  M.D., 
  F.G.S. 
  

   (Bead 
  December 
  19, 
  1888.) 
  

  

  A 
  eexe 
  yellow 
  clay 
  which 
  occurs 
  in 
  Jersey 
  and 
  in 
  at 
  least 
  some 
  of 
  the 
  

   other 
  Channel 
  Islands 
  has 
  received 
  little 
  attention 
  from 
  geologists, 
  

   and 
  the 
  few 
  who 
  have 
  noticed 
  it 
  appear 
  to 
  have 
  considered 
  it 
  

   merely 
  the 
  result 
  of 
  local 
  weathering. 
  This 
  clay 
  is 
  more 
  or 
  less 
  

   sandy, 
  and 
  though 
  generally 
  of 
  a 
  dull 
  yellow 
  colour, 
  is 
  sometimes 
  

   reddish 
  orange. 
  On 
  microscopic 
  examination 
  many 
  of 
  the 
  grains 
  

   are 
  seen 
  to 
  he 
  somewhat 
  rounded, 
  but 
  the 
  majority 
  of 
  them 
  have 
  sharp 
  

   angles. 
  In 
  one 
  or 
  two 
  situations 
  the 
  clay 
  effervesces 
  freely 
  with 
  acids, 
  

   and 
  at 
  some 
  places 
  on 
  the 
  coast 
  it 
  has 
  been 
  found 
  to 
  coat 
  the 
  grass 
  

   roots 
  with 
  a 
  pipe-like 
  covering. 
  On 
  a 
  small 
  detached 
  island 
  on 
  the 
  

   south-east 
  coast 
  it 
  contains 
  fantastically-shaped 
  concretions 
  like 
  the 
  

   "Mdnnehen" 
  of 
  the 
  Bhenish 
  loss. 
  This, 
  however, 
  is 
  probably 
  due 
  

   to 
  the 
  fact 
  that 
  above 
  the 
  clay 
  at 
  this 
  point 
  there 
  is 
  a 
  bed 
  of 
  shells, 
  

   all 
  modern, 
  from 
  which 
  carbonate 
  of 
  lime 
  has 
  been 
  washed 
  down 
  by 
  

   rain. 
  Sometimes 
  the 
  clay 
  exhibits 
  obscure 
  marks 
  of 
  bedding, 
  and 
  

   at 
  one 
  point 
  in 
  the 
  town 
  of 
  St. 
  Helier, 
  where 
  an 
  excavation 
  had 
  

   been 
  made 
  for 
  relaying 
  some 
  drains, 
  I 
  noticed 
  distinct 
  lamination. 
  

   Mr. 
  Green, 
  a 
  well-sinker, 
  has 
  also 
  told 
  me 
  that, 
  in 
  sinking 
  wells, 
  he 
  

   has 
  often 
  noticed 
  distinct 
  stratification. 
  The 
  lower 
  part 
  of 
  the 
  

   clay 
  often 
  contains 
  angular 
  stones, 
  sometimes 
  grouped 
  together 
  

   pretty 
  closely, 
  sometimes 
  at 
  some 
  distance 
  from 
  each 
  other, 
  while 
  

   occasionally 
  a 
  single 
  stone, 
  or 
  one 
  or 
  two, 
  may 
  be 
  noticed, 
  with 
  no 
  

   others 
  within 
  some 
  distance. 
  These 
  stones 
  generally 
  vary 
  in 
  size 
  

   from 
  an 
  inch 
  or 
  two 
  to 
  about 
  a 
  foot 
  in 
  their 
  longest 
  diameter, 
  but 
  

   now 
  and 
  then 
  a 
  piece 
  of 
  rock 
  two 
  or 
  three 
  feet 
  or 
  more 
  in 
  its 
  greatest 
  

   length 
  may 
  be 
  noticed. 
  In 
  most 
  cases 
  these 
  stones 
  lie 
  with 
  their 
  

   longest 
  diameter 
  parallel 
  to 
  the 
  surface 
  of 
  the 
  rock 
  below, 
  but 
  

   often 
  they 
  are 
  observed 
  to 
  be 
  more 
  or 
  less 
  upright. 
  One 
  section 
  

   shows 
  a 
  layer 
  of 
  small 
  stones 
  running 
  for 
  about 
  six 
  or 
  eight 
  feet, 
  

   and 
  some 
  feet 
  above 
  the 
  bottom 
  of 
  the 
  clay. 
  All 
  these 
  fragments 
  

   are 
  of 
  the 
  same 
  nature 
  as 
  the 
  subjacent 
  rock, 
  or 
  are 
  derived 
  from 
  

   some 
  rock 
  bed 
  far 
  distant. 
  

  

  The 
  rocks 
  of 
  the 
  island 
  are 
  chiefly 
  igneous, 
  viz. 
  granite, 
  diorite, 
  

   rhyolite, 
  quartz-felsite. 
  and 
  a 
  trachytic-looking 
  porphyry 
  : 
  but 
  an 
  

   argillaceous 
  shale, 
  in 
  places 
  hardened 
  and 
  altered 
  by 
  heat, 
  is 
  found 
  

   largely 
  developed 
  over 
  considerable 
  areas, 
  and 
  a 
  conglomerate 
  con- 
  

   sisting 
  of 
  fragments 
  of 
  this 
  rock 
  is 
  found 
  on 
  the 
  north-east 
  corner 
  

   of 
  the 
  island. 
  The 
  later 
  geology 
  is 
  represented 
  by 
  raised 
  beaches 
  

   and 
  by 
  submerged 
  forest-beds 
  and 
  peat. 
  There 
  are 
  two 
  well- 
  

   marked 
  raised 
  beaches 
  between 
  fifty 
  and 
  sixty 
  feet 
  above 
  mean 
  

   tide-level 
  ; 
  and 
  there 
  is 
  a 
  cup-shaped 
  depression, 
  apparently 
  the 
  

   section 
  of 
  a 
  gulley, 
  at 
  the 
  top 
  of 
  the 
  rocky 
  side 
  of 
  a 
  granite 
  outlier, 
  

   some 
  150 
  feet 
  above 
  mean 
  tide-level, 
  which 
  contains 
  a 
  deposit 
  of 
  

   well-rounded 
  pieces 
  of 
  granite, 
  as 
  well 
  as 
  other 
  angular 
  blocks. 
  

  

  